1. Field of the Invention
The invention relates to a storage apparatus, a method of controlling the same, and a program for causing a computer to carry out the method. More particularly, the invention relates to a storage apparatus such as a network attached storage (NAS) apparatus, including a plurality of nodes each including first and second memories in order to store data stored in the first memory into the second memory as backup data, a method of controlling a network attached storage apparatus, and a program for causing a computer to carry out the method.
2. Description of the Related
For instance, Japanese Patent Application Publication No. 2004-213435 has suggested a NAS system including a plurality of NAS nodes, a cache memory commonly used by the NAS nodes, and a battery for supplying electrical power to the cache memory. Read/write data transmitted from a client apparatus to each of the NAS nodes is temporarily stored in the cache memory, and then, written into a disc. In the suggested NAS system, the cache memory is backed up by a battery to ensure that data stored in the cache memory is protected even when any one of the NAS nodes is troubled.
However, the suggested NAS system is accompanied with a problem that the NAS system has to include a cache memory having a large capacity and operating at a high speed, resulting in high costs. Hence, the suggested NAS system can be used only in a high-end apparatus.
Japanese Patent Application Publication No. 2001-34535 has suggested a cache memory backup system in which when data is written into a cache memory, the same data is written further into a non-volatile memory, taking precaution against that a power supply is turned off while data is being written into the cache memory.
Japanese Patent Application Publication No. 5-225074 (published September 1993) has suggested a memory system including first and second modules each including a cache memory, a non-volatile memory, and a power source. Amended block of data is written into both a cache memory of the first module and a non-volatile memory of the second module, ensuring that data is protected even if a power source of one of the first and second modules is troubled.
When the memory system suggested in Japanese Patent Application Publication No. 5-225074 is applied to a NAS apparatus, each of nodes is designed to include a cache memory, a non-volatile memory, a copier for copying data stored in a cache memory in a first node into a non-volatile memory in a second node, and a copier-interface through which data stored in a cache memory in first and second nodes are transmitted to each other. For instance, if the copier-interface is troubled, it would be impossible to identify which copier is troubled among the copiers in the first and second nodes.
In such a case, for instance, the first node is ceased to operate, and the second node takes over tasks to be carried out by the first node, that is, the second node fails over the first node. Then, a copier of the first node is exchanged into a new one, and thereafter, the first node restarts.
However, if a copier of the second node is actually in trouble, there occurs a copier-interface trouble again, even if a copier of the first node is exchanged into a new one, and then, the first node restarts, resulting in that the first node is ceased to operate again. It is necessary to completely cease operation of the NAS apparatus, and exchange a copier of the second node into a new one.
Japanese Patent Application Publication No. 6-222988 (published August 1994) has suggested a memory controller including a first cluster device through which data is transmitted to a memory from a host computer, a second cluster device through which data is transmitted to a memory from a host computer, a first cache memory electrically connected to the first cluster device, a second cache memory electrically connected to the second cluster device, a first non-volatile memory electrically connected to the second cluster device, a second non-volatile memory electrically connected to the first cluster device, a first unit which stores data into the first cache memory, and stores the data into the first non-volatile memory as backup data, and a second unit which reads the data out of the first non-volatile memory when the first cache memory is troubled.
Japanese Patent Application Publication No. 2000-278286 has suggested a network system including two networks independent of each other, and a plurality of nodes each making communication with the networks. Each of the nodes includes a monitoring device which monitors whether a predetermined node is making communication with the networks, a channel administrator which administrates channels through which communication is made among the nodes, and a selector which selects one of the networks for communication among the nodes.
Japanese Patent Application Publication No. 2003-162439 has suggested a storage system including a plurality of interfaces, a plurality of discs accessible from the interfaces, and a common memory accessible from the interfaces. Each of the interfaces includes a block interface dealing with an I/O request per a disc block and/or a file interface having a file server dealing with an I/O request per a file. A file system commonly accessible from a plurality of file servers is constructed in a part of the discs. The common memory has a first area in which a changing log of the file system is stored, and a second area in which data relating to an administration file server is stored.